Dental implants are used as replacements for missing teeth. Implants are typically in the form of a fixture that is coupled to an abutment. The fixture portion of a dental implant is that portion which extends into the maxilla or mandible, where it is anchored in a bone in the maxilla or mandible. The fixture typically includes a top portion that extends out of the maxilla or mandible and provides an anchoring point for an abutment. The abutment portion of a dental implant is the portion that is fixed to the fixture and extends above the gingiva. It has an upper surface that is configured to receive and support a crown.
There are several common problems with such two piece dental implants. First, the bone into which they are inserted often does not bond (e.g. integrate) well with the implant, or, if bonded, degrades causing the implant to loosen over time.
Microgaps between the fixture and the abutment are one cause of this loss of bone. The fixture is often positioned within the maxilla or mandible such that its upper surface is below the gingiva. When an abutment is fixed to the fixture, there is a tiny gap between the abutment and the fixture that is at least partially disposed beneath the gingiva. This microgap becomes a haven or reservoir for oral bacteria. By cultivating oral bacteria so close to the fixture/bone junction itself, the gingiva may become irritated or infected, and the bond between the fixture and the maxilla or mandible weakened. Loosening may also be caused by the poor distribution of forces from the implant to the maxilla or mandible. If the load is concentrated on a particular portion of the maxilla or mandible, this stress concentration may cause the bond between fixture and maxilla or mandible to weaken. Stress concentrations are typically caused by improper fixture design or positioning, or a fixture that is not shaped to distribute the tooth load relatively evenly.
Another problem often encountered with implants is the failure of the crown that is attached to the abutment. Large loads placed on the crown when chewing cause the crown to fatigue and ultimately to fracture. These large loads can also weaken the cement that bonds the crown to the abutment if the crown-to-abutment joint design unduly concentrates the load.
What is needed, therefore, is an improved dental implant that reduces the chance of infection and fixture loosening. It is an object of this invention to provide such a dental implant that alleviates these problems in one or more of the illustrated embodiments